Auto-workletize functions passed to runOnUI

[tomekzaw]

Summary

This PR adds runOnUI to the list of automatically workletized functions as suggested by @kacperkapusciak.

Previously, the following code:

runOnUI(() => {
  console.log('Hello from the UI thread!');
})();

would throw the following error:

Error: runOnUI() can only be used on worklets, js engine: hermes

because the function passed to runOnUI needs to be marked as worklet:

 runOnUI(() => {
+  'worklet';
   console.log('Hello from the UI thread!');
 })();

After this change, the 'worklet'; directive can be omitted and the function will be automatically workletized by the Reanimated Babel plugin.

Test plan

App.tsx

import { Button, StyleSheet, View } from 'react-native';

import React from 'react';
import { runOnUI } from 'react-native-reanimated';

export default function App() {
  const handlePress = () => {
    runOnUI(() => {
      console.log('Hello from the UI thread!');
    })();
  };

  return (
    <View style={styles.container}>
      <Button title="Click me" onPress={handlePress} />
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    alignItems: 'center',
    justifyContent: 'center',
  },
});

[tjzel]

While I agree that this change is a natural extension of what we have already done, I wonder if runOnUI has many common use cases. I always thought we should keep the 'worklet' directive here as necessary due to the fact that using this function has its limitations and should be used only when one has a deeper understanding of Reanimated. For example:

runOnUI(() => {
  'worklet';
  console.log('Hello from the UI thread!');
  runOnUI(() => {
    'worklet';
    console.log("Hello again with 'worklet'!");
  })();
})();

and

runOnUI(() => {
  'worklet';
  console.log('Hello from the UI thread!');
  runOnUI(() => {
    // Missing 'worklet' directive
    console.log("Hello again without 'worklet'!");
  })();
})();

Both will crash. If you consider this limitation unrelated to whether we should be forced to type 'worklet' or not, I'm open to approving this.

[tjzel]

How about adding one or two unit tests for this?